Can a mans DNA sample be used for other DNA tests on other children by different mohters?

Someone is claiming my husband as their baby's father. We got paperwork in the mail to call someone, which we did, to see what needed to be done next. He has been to the same place to do a DNA test before, on one of our children. The people we spoke with stated that his DNA sample was on file because of this and he would not need to come in and do another sample. However, a lot of people are telling us that there is no way this can be done. The appropriate people are telling us no, he does not need to but we were wanting information on the correct way DNA is done and if the sample can be used again so he does not get into any trouble.